WP-CRM - CRM solution for WordPress.
Appointment Booking Calendar - With the Appointment Booking Calendar you can accept online bookings from a set of available time-slots in the calendar.
CozyCal - Online appointment scheduling
MakePlans - Online appointment booking - MakePlans
vCita - Online client engagement solution, convert website visitors to clients, free customizable contact form, free online appointment scheduler.
Dudle - Dudle is an online scheduling application, which is free and open source.